Relay selection in cooperative communication systems over continuous time-varying fading channel

In this paper, we study relay selection under outdated channel state information (CSI) in a decode-and-forward (DF) cooperative system. Unlike previous researches on cooperative commu-nication under outdated CSI, we consider that the channel varies continuously over time, i.e., the channel not only changes between relay selection and data transmission but also changes during data transmission. Thus the level of accuracy of the CSI used in relay selection degrades with data transmission. We first evaluate the packet error rate (PER) of the cooperative system under contin-uous time-varying fading channel, and find that the PER performance deteriorates more seriously under continuous time-varying fading channel than when the channel is assumed to be constant during data transmission. Then, we propose a repeated relay selection (RRS) strategy to improve the PER performance, in which the forwarded data is divided into multiple segments and relay is reselected before the transmission of each segment based on the updated CSI. Finally, we propose a combined relay selection (CRS) strategy which takes advantage of three different relay selection strategies to further mitigate the impact of outdated CSI.     

一种基于压缩感知的信道估计算法

信道估计是无线通信系统的关键技术之一。文章提出一种基于压缩感知（Compressed Sensing）的信道估计方法,这种方法通过分析信道时延和多普勒域的稀疏度,可以有效降低导频的数量,从而提高系统的频谱利用率。通过与最小均方（Least Square,LS）信道估计方法的对比,可以明显看到导频数量的降低。     

CCSDS图像无损压缩标准在恒速信道中的应用研究

在CCSDS建议的无损数据压缩的基本原理上 ,结合基于局域纹理特征的处理方法 ,给出数据输入输出在恒速信道条件下一种有效的面向空间应用的遥感图像无损压缩方案。该方案包括去相关处理、熵编码以及压缩缓存控制三部分。去相关操作是在局域纹理分析方法的基础上 ,通过提取两种有效的预测模型并自适应选择最佳的模型进行处理 ;然后采用快速有效的CCSDS熵编码器对最佳去相关模型的预测误差编码。在压缩方案中充分考虑了输入输出恒速信道条件下应用的特殊性 ,设计了相应的压缩码流控制方法 ,从而给出了一套有效的针对恒速输入输出信道条件下的图像无损压缩的应用方案     

Rician衰落信道下Turbo码性能分析

文中研究了Rician信道下Turbo码的性能,并详细推导Turbo码在Rician信道下的误码率上界的表达 式,最后对Rician信道的主要参数对译码性能的影响作了仿真。     

Location-aware channel estimation for capacity gains on multibeam satellite links

Bandwidth is an expensive and scarce resource, thus its efficient exploitation is of paramount importance. Recent communication satellites feature sophisticated spatial access strategies through spot beams providing this way a total throughput in the range of 100 Gbit/s. Next generations of communication satellites, as postulated in the Satellite Communications Network of Experts (SatNEx) III, a project funded by the European Space Agency (ESA) for advanced research in satellite communications, require technological developments to achieve the Tbit/s region. Multibeam architectures formed by a central gateway, a multibeam satellite, and an aggressive frequency reuse strategy can meet such ambitious design goals. Interference problems are tackled by appropriate countermeasures such as (joint) precoding and beamforming on the forward link as well as multi-user detection on the return link; these methods require accurate and timely knowledge of the channel state, which in turn necessitates suitable algorithms for channel estimation. This paper addresses performance issues related to channel state estimation on the symbol-synchronous forward link and the frame-synchronous return link. It highlights for both directions the potential performance gain by assuming a priori knowledge of the user position, in this context referred to as location-aware channel estimation.     

Prediction of horizontal gas–solid flows under different gravitational fields

In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.     

X波段遥感数传微波通道

遥感数传微波通道是数传遥感卫星的发射系统,是实现地物信息实时传输的重要设备。为了实现高码速率的传输,分别利用上边带上变频器和下边带上变频器将传输的微波信道分成两个信道,每个信道传输53Mbit/s,两个信道可传输的码速率为106Mbit/s。文章介绍了单信道微波通道和双信道微波通道,并扼要地介绍了微波通道中的上变频器和阶跃管电抗开关倍频器。     

信道状态信息无线感知数据获取及应用综述

近年来,基于信道状态信息（CSI）的无线感知技术在室内定位、活动识别、健康检测等方向有众多探索性研究应用。然而,现有研究获取CSI数据主要依靠自主采集,对CSI开源数据集和数据采集设备/工具的研究现状不够清晰。首先阐述了基于无线保真（WiFi）CSI的无线感知技术,详细介绍了9种CSI数据采集设备/工具,概括了CSI的应用方向及研究现状,并汇总了近5年的CSI开源数据集,分析了现有CSI无线感知研究的局限性与面临的挑战,最后总结全文并对CSI无线感知未来的发展进行展望。     

分布式电能计量与计费系统中通信信道特性与实现方案的研究

本文介绍了分布式电能计量与计费系统中低压电力线作为载波通信信道时的信道特性，给出了实验数据和特性曲线，并选择了通信的基本方案。     

我国早期原子钟研制历程回顾

“2019全国时间频率学术会议”是由四个专业委员会联合每两年举办一次的20周年纪念会。20年来，我国原子钟事业已有长足发展，成为世界上原子钟研制与开发的大国。但总体上说，我们的工作还是以跟随为主，真正属于自主创新的较少。不改变这种局面，我们还难以成为独立自主的时间频率强国，为国家经济和国防建设作出应有贡献。本文回顾了我国原子钟研发的情况，提到一些从基础研究上属于原始创新的案例。阐述了这些案例是在简陋的实验条件下依靠对原子钟内各类实验现象进行深入的物理分析基础上出现的。同时，也指出了在比较粗糙的工艺条件下实现精细的技术指标中能工巧匠所起的特殊作用。文章也约略提到国内各单位间无私协作的崇高精神。本文将讲述一些故事，并就原子钟产业的问题表示一点看法。中国要实现“强国梦”，阻力和困难还很多很艰巨，我们必须拥有丰富的原始创新来加以克服。为此，坚韧的奋斗钻研精神和传统仍不失借鉴与继承意义。